Drafting assembly and method of drafting a web

ABSTRACT

A drafting assembly for drafting a fibre web having upper and lower rear apron loops which have first and second support surfaces respectively being arranged to grip the card web fibres between them and transport the card web fibres from a rear entrance to a rear nip point on displacement of the rear aprons. Upper and lower front apron loops have third and fourth support surfaces, respectively, being arranged to grip the card web fibres between them and transport the card web fibres from a front nip point to an exit on displacement of the front aprons. The front and rear nip points are adjacent and arranged such that the front nip point receives card web fibres which exit the rear nip point. Proximate to the nip point, each loop is wedge shaped with the arms of the loop on each side of the nip point converging towards nip point and having an acute angle therebetween.

The present invention relates to a drafting assembly and method of drafting. More particularly, but not exclusively, the present invention relates to a drafting apparatus comprising two pairs of drafting aprons separated by a gap and arranged to generate a drafting force on fibres in a web which span the gap; the drafting aprons each being substantially wedge shaped proximate to the nip points.

It is known to draft slivers, rovings or strands by roller drafting. The drafting apparatus comprises front and rear roller pairs. The front roller pair rotate more quickly than the rear pair so creating a drafting force on the fibres in the sliver or strand.

Such an apparatus is suitable for drafting slivers, rovings or strands since the sliver, roving or strand is thick enough or is immediately twisted so there is little problem of the fibres lapping around the front rollers. It is also known to draft card webs. Fibres in a card web are less consolidated and require larger rollers to prevent lapping. Fibres in a card web are also not aligned. It has been found that drafting the fibres in the card web, by a relatively small draft whilst in the web state or at least in an open state in comparison to the sliver, followed by the normal process of producing the sliver package for the combing machine has a beneficial effect of better preparing the sliver package as it results in a reduction in the noil extracted by the combing machine. Furthermore, there is evidence that such drafting of the card web results in overall higher quality of yarn. It appears that such a process of web drafting partially or in some cases completely removes hooks but also re-arranges the fibres so that the subsequent drafting is more efficient in removing hooks that remaining the material.

In order for this drafting to be beneficial, it is essential that drafting occurs whilst the fibres including short fibres, remain under positive control as far as possible. For the avoidance of doubt it should be stated that reference here to long and short fibres does not refer to the intrinsic length of the fibres but the extension of the fibres along the length of the web. For example an intrinsically long fibre may be looped or twisted upon itself or may be inclined to the length of the web. In such cases an intrinsically long fibre may be classed as a short fibre.

Apparatus for the drafting of card webs are restricted to drafting of worsted type long fibres, since it permits the use of relatively large rollers which prevent fibre lapping of rollers whilst having sufficient control of the fibres in drafting. One cannot simply reduce the diameter of the rollers to provide sufficient control in card web drafting of shorter cotton type fibres because of this problem of fibre lapping.

Existing drafting assemblies are therefore unsuitable for drafting cotton type card webs.

The present invention seeks to alleviate this problem.

Accordingly, in the first aspect, the present invention provides:

-   -   a drafting assembly for drafting a fibre web, the drafting         assembly comprising:     -   upper and lower rear apron loops having first and second support         surfaces respectively being arranged to grip card web fibres         between them and transport the card web fibres from a rear         entrance to a rear nip point on displacement of the rear aprons;     -   upper and lower front apron loops having third and fourth         support surfaces respectively being arranged to grip the card         web fibres between them and transport the card web fibres from a         front nip point to an exit on displacement of the front aprons;     -   the front and rear nip points being adjacent and arranged such         that the front nip point receives card web fibres which exit the         rear nip point;     -   characterised in that     -   proximate to the nip point each loop is wedge shaped with the         arms of the loop on each side of the nip point converging         towards nip point and having an acute angle there between.

The wedge shaped nature of the apron loops proximate to the nip point enables cotton type card web to be drafted, so significantly improving the properties of the drafted web. Preferably the arms of at least one of the loops on each side of the nip point are substantially planar.

Preferably, the drafting assembly further comprises a drive assembly for displacing the aprons, the drive assembly being adapted to displace the front aprons more rapidly than the rear aprons so generating a drafting force on the fibres in the web gripped by the front and rear nip points.

At least one of the aprons can comprise a planar portion defining a support surface. The loop can be nylon, PVC or rubber, preferably reinforced rubber. The loop can be a composite material. The loop can be polyurethane.

Preferably, the drafting assembly comprises upper and lower rear nip rollers arranged to nip the upper and lower rear aprons between them to create the rear nip point. Alternatively the drafting assembly could comprise upper and lower rear nip bars arranged to nip the upper and lower rear aprons between them to create the rear nip point. The drafting assembly could also comprise upper and lower front nip rollers arranged to nip the upper and lower front aprons between them to create the front nip point. Alternatively, the drafting assembly could comprise upper and lower front nip bars arranged to nip the upper or lower front spans between them to create the front nip point.

The drive assembly can comprise at least one drive roller which abuts an apron and is adapted to displace the apron on rotation of the drive roller. The drive roller can be positioned within the loop.

In a further aspect of the invention there is provided a carding assembly comprising

-   -   at least one carding roller for creating a fibre web; and     -   a drafting assembly for drafting the fibre web     -   the drafting assembly comprising     -   upper and lower rear apron loops having first and second support         surfaces respectively being arranged to grip the fibre web         between them and transport the web from a rear entrance to a         rear nip point on displacement of the rear aprons;     -   upper and lower front apron loops having third and fourth         support surfaces respectively being arranged to grip the fibre         web between them and transport the web from a front nip point to         an exit on displacement of the front aprons;     -   the front and rear nip points being adjacent and arranged such         that the front nip point receives fibre web which exits the rear         nip point;     -   characterised in that     -   proximate to the nip point each loop is wedge shaped with the         arms of the loop on each side of the nip point converging         towards nip point and having an acute angle therebetween.

The carding assembly can further comprise consolidating means for partially reducing the width of the web before it is received by the drafting assembly. The carding assembly could also comprise a further consolidating means for receiving the drafted web from the drafting assembly and further reducing its width to a sliver.

In a further aspect of the invention there is provided a method of drafting a fibre web comprising the steps of

(a) providing a drafting apparatus, the drafting apparatus comprising

-   -   upper and lower rear apron loops having first and second support         surfaces respectively being arranged to grip the fibre web         between them and transport the web from a rear entrance to a         rear nip point on displacement of the rear aprons;     -   upper and lower front apron loops having third and fourth         support surfaces respectively being arranged to grip the fibre         web between them and transport the web from a front nip point to         an exit on displacement of the front aprons;     -   the front and rear nip points being adjacent and arranged such         that the front nip point receives fibre web which exits the rear         nip point;     -   characterised in that     -   proximate to the nip point each loop is wedge shaped with the         arms of the loop on each side of the nip point converging         towards nip point and having an acute angle therebetween.         (b) providing a fibre web to the drafting apparatus for         drafting.

The present invention will now be described by way of example only, and not in any limitative sense with reference to the accompanying drawings in which

FIGS. 1 and 2 show, in schematic form, drafting assemblies for drafting slivers, rovings or strands;

FIGS. 3 and 4 show further known drafting assemblies in cross section;

FIG. 5 shows a further known drafting assembly in cross section;

FIG. 6 shows a drafting assembly according the invention in cross section; and

FIG. 7 shows a carding assembly according to the invention.

A number of different types of machine are known for processing cotton type and worsted type fibres into yarn. In general these machines provide the steps of:

(1) The opening, cleaning and reducing fibres to small tufts; (2) “carding” the fibres to open or individualise fibres. This process forms a web of fibres which is consolidated at the output end into a rope like form called a sliver; and, (3) aligning the disordered carded fibres and progressively reducing the sliver thickness or linear density by a series of machines until in the final “spinning” machine a strand of fibres is formed which is consolidated by twisting to form a yarn.

Short fibres are not conducive to the production of high quality yarns. The yarns are therefore combed to remove these. Combing takes place after carding but before spinning.

The fibres need to be aligned before they can be subjected to the combing process. This is done by drafting.

Shown in FIGS. 1 and 2 in schematic form are known as roller drafting assemblies (1). The drafting assembly (1) of FIG. 1 comprises a pair of front rollers (2) and a pair of rear rollers (3). The front rollers (2) are arranged to rotate more rapidly than the rear rollers (3) so producing a drafting force on the fibres (4) as they move between the two sets of rollers (2, 3). The assembly (1) shown in FIG. 2 includes a pair of rear aprons (5, 6) for better control of fibres.

Roller drafting is typically performed on slivers and rovings or occasionally on card webs. It is known that a large proportion of the fibres in the card sliver or web are hooked as a result of the carding process. Hook free material can lead to better quality of yarn and/or lower the amount of comber waste. The assemblies of FIGS. 1 and 2 are however only suitable for drafting of slivers and rovings. The consolidated nature of slivers and rovings reduces the tendency of the fibres to lap around the rollers. The apparatus of FIGS. 1 and 2 are not suitable for drafting card web fibres. This is because fibres in the web are less consolidated and can lap more easily. If the apparatus of FIG. 2 were to be used to draft card webs the diameter of the rollers would have to be large to reduce fibre lapping. This would however increase the distance between the nip points to an unacceptable degree.

Shown in FIGS. 3 and 4 are further known drafting assemblies. These assemblies are attempts to overcome this problem. Each of the assemblies comprises upper and lower rear aprons (7, 8). The upper and lower rear aprons (7, 8) each comprise a flexible loop of material (9, 10), typically pvc, nylon, rubber, polyurethane or a composite material. Positioned within each loop (9, 10) is a drive assembly (11, 12) comprising a drive roller (13, 14) which abuts the loop (9, 10). Turning the drive roller (13, 14) turns the loop (9, 10). Each of the aprons (7, 8) includes a planar support portion (15, 16). The two planar support portions (15, 16) are arranged to grip the fibres of a sliver received at an entrance (17) between them. As the drive rollers (13, 14) turn the fibres of the input fibre sliver are drawn from the entrance (17) to a rear nip point (18). The rear nip point (18) is created by upper and lower rear nip rollers (19, 20) which nip the upper and lower aprons (7, 8) between them.

The embodiment of FIG. 3 does not include a front apron and is generally used for drafting worsted card slivers. The drafting assembly of FIG. 4 further comprises a front apron (21) in the form of a loop (22) having a shape defined by tensioning means (23). In the drafting assembly of FIG. 4 a lower front nip roller (24) is positioned within and abuts against the front apron loop (22). An upper nip roller (25) nips the apron (21) between it and the lower nip roller (24) creating a front nip point (26). The front and rear nip points (26, 18) are arranged such that the fibres which exit the rear nip point (18) are received by the front nip point (26).

Such drafting assemblies can be used for sliver drafting or worsted type web drafting. However, again they are not suitable for drafting cotton type card webs as the distance between the nip point is unacceptably large.

The reduction in size of one of the front nip point rollers partially reduces the distance between front and rear nip points and is suitable for worsted type card web drafting. The relatively large upper nip rollers (25) in FIGS. 3 and 4, necessary to avoid fibre lapping, places a limit on how close together the front and rear nip point (26, 18) can be. This in turn places a relatively large lower limit on the length of fibre which can be controlled in the drafting process. Fibres below this limit either because of their length or because of their relative orientation or configuration will tend to be uncontrolled. However, reducing of the size of the upper front drafting roller would result in the fibres from the web lapping around the roller. Because of this such apparatus is not suitable for drafting cotton type card web.

Shown in FIG. 5 is an assembly similar to that of FIG. 2. Like reference numerals are used for like parts. Further aprons are arranged around the front rollers. Such a system is disclosed in DE 4141237. The use of further aprons in such systems is to carry the fibres forward to further rollers in some arrangement that improves yarn quality. Such assemblies are also not suitable for drafting cotton type card webs. One cannot simply reduce the front rollers to reduce the distance between the nip points. As the roller diameters are reduced to the levels required for effective drafting of cotton type cad webs the rollers become difficult to drive.

Shown in FIG. 6 is a drafting assembly according to the invention. The drafting assembly comprises upper and lower rear aprons (27, 28). The drafting assembly further comprises upper and lower front aprons (29, 30) in the form of loops. Associated with each apron (27-30) is a drive assembly (31) within the loop. Each drive assembly (31) comprises a drive roller (32) which abuts against the inside of each respective loop and which drives rotation of the loop. The upper and lower front aprons (29, 30) have third and fourth support surfaces (33, 34) respectively. These are arranged to grip the fibre web received at a front nip point (35) and transport it to an exit point (36).

The front nip point (35) is created by upper and lower front nip rollers (37, 38). These nip the upper and lower front aprons (29, 30) between them. The rear nip point is created by upper and lower rear nip rollers.

In use the above drive assembly (31) rotates the upper and lower rear aprons (27, 28) transporting the web from the entrance (39) to the rear nip point (40). The web exits the rear nip point (40) and is received by the front nip point (35). From here it is transported to the exit point (36). The drive rollers (32) rotate the front aprons (29, 30) more rapidly than the rear (27, 28) so producing a drafting action on fibres as they span the gap between the front and rear nip points (35, 40). The aprons close to the nip points are arranged to be wedge shaped with the arms of the apron on each side of a nip roller converging toward the nip roller and having an acute angle between them. The wedge shaped aprons on opposite sides of the nip points face each other. In this embodiment the arms are planar. This wedge shaped arrangement allows the front and rear nip points to be positioned close together. The apparatus according to the invention can use small front rollers. The aprons avoid the problem of fibre lapping. The arrangement of the aprons results in a short distance between the nip points and rollers which are relatively easy to drive. The apparatus can therefore be used to draft shorter fibres under control in webs than known drafting apparatus. This results in a commercially significant improvement in the web with a significant reduction in noil in the subsequent combing process.

Shown in FIG. 7 is a carding assembly (41) according to the invention. The carding assembly (41) comprises a carding roller (42) for producing a web which is received by the drafting assembly of FIG. 6. Arranged between the carding roller (42) and drafting assembly is a consolidating means (not shown). The consolidating means reduces the width of the web. The web is however still maintained wider and more open than a sliver.

In a further embodiment of the invention (not shown) the carding assembly comprises a further consolidating means which further consolidates the drafted web as it leaves the drafting assembly.

In a further embodiment of the invention (not shown) the carding assembly does not include a consolidating means for reducing the width of the web.

In a further embodiment of the invention (not shown), the nose rollers are replaced by nose bars. This however reduces the drafting speed. 

1. A drafting assembly for drafting fibre web, the drafting assembly comprising: upper and lower rear apron loops having first and second support surfaces respectively being arranged to grip the card web fibres between them and transport the card web fibres from a rear entrance to a rear nip point on displacement of the rear aprons; upper and lower front apron loops having third and fourth support surfaces respectively being arranged to grip the card web fibres between them and transport the card web fibres from a front nip point to an exit on displacement of the front aprons; the front and rear nip points being adjacent and arranged such that the front nip point receives card web fibres which exit the rear nip point; characterised in that proximate to the nip point each loop is wedge shaped with the arms of the loop on each side of the nip point converging towards nip point and having an acute angle therebetween.
 2. A drafting assembly as claimed in claim 1, when the arms of at least one of the loops on each side of the flip point is substantially planar.
 3. A drafting assembly as claimed in claim 1 further comprising a drive assembly for displacing the aprons, the drive assembly being adapted to displace the front aprons more rapidly than the rear aprons so generating a drafting force in fibres in the web gripped between the front and rear nip points.
 4. A drafting assembly as claimed in claim 1, at least one of the aprons comprising a planar portion defining the support surface.
 5. A drafting assembly as claimed in claim 4 wherein the loop is nylon, PVC, polyurethane or rubber, preferably reinforced rubber.
 6. A drafting assembly as claimed in claim 1 further comprising upper and lower rear nip rollers arranged to nip the upper and lower rear aprons between them to create the rear nip point.
 7. A drafting assembly as claimed in claim 1, further comprising upper and lower rear nip bars arranged to nip the upper and lower rear aprons between them to create the rear nip point.
 8. A drafting assembly as claimed in claim 1 further comprising upper and lower front nip rollers arranged to nip the upper and lower front aprons between them to create the front nip point.
 9. A drafting assembly as claimed in claim 1 further comprising upper and lower front nip bars arranged to nip the upper and lower front aprons between them to create the front nip point.
 10. A drafting assembly as claimed in claim 2 wherein the drive assembly comprises at least one drive roller which abuts the apron and is adapted to displace the apron on rotation of the drive roller.
 11. A drafting assembly as claimed in claim 10 wherein the drive roller is positioned within the loop.
 12. A carding assembly comprising at least one carding roller for creating a fibre web; and a drafting assembly for drafting the fibre web the drafting assembly comprising upper and lower rear apron loops having first and second support surfaces respectively being arranged to grip the fibre web between them and transport the web from a rear entrance to a rear nip point on displacement of the rear aprons; upper and lower front apron loops having third and fourth support surfaces respectively being arranged to grip the fibre web between them and transport the web from a front nip point to an exit on displacement of the front aprons; the front and rear nip points being adjacent and arranged such that the front nip point receives fibre web which exits the rear nip point; characterised in that proximate to the nip point each loop is wedge shaped with the arms of the loop on each side of the nip point converging towards nip point and having an acute angle therebetween.
 13. A carding assembly as claimed in claim 12 comprising consolidating means for partially reducing the width of the web before it is received by the drafting assembly.
 14. A carding assembly as claimed in claim 13 comprising a further consolidating means for receiving the drafted web from the drafting assembly and further reducing its width to a sliver.
 15. A method of drafting a fibre web comprising the steps of providing a drafting apparatus, the drafting apparatus comprising upper and lower rear apron loops having first and second support surfaces respectively being arranged to grip the fibre web between them and transport the web from a rear entrance to a rear nip point on displacement of the rear aprons; upper and lower front apron loops having third and fourth support surfaces respectively being arranged to grip the fibre web between them and transport the web from a front nip point to an exit on displacement of the front aprons; the front and rear nip points being adjacent and arranged such that the front nip point receives fibre web which exits the rear nip point; characterised in that proximate to the nip point each loop is wedge shaped with the arms of the loop on each side of the nip point converging towards nip point and having a acute angle therebetween; and (b) providing a fibre web to the drafting apparatus for drafting. 